|Events during May
· 26th - Mercury is at greatest western elongation (25º).
· The Moon: New - 14th, Full - 27th.
Apogee (404,230 kilometres) - 6th, Perigee (369,730 kilometres) - 20th.
Mercury reaches greatest western elongation (25º) on May 26th and, towards the end
of the month, becomes visible for observors in tropical and southern latitudes. For southern observors this is the most favourable morning apparition
During this period of visibility, which began in late March, Mercury fades from -1.4 to +1.0 magnitude. The brilliant Venus will be in the same part
of the sky as Mercury and is a useful guide to locating the fainter planet. In Europe and north America, between the 3rd and 8th April, at the end of
evening twilight Venus and Mercury will be at the same altitude above the horizon with Venus slightly further to the west and 25 times brighter than Mercury.
The best times to observe Mercury in the northen hemisphere are when it is an evening star in the spring and a morning star in the autumn. In midsummer
the lighter skies make visibility difficult near the horizon.
Venus is a brilliant -4.0 magnitude in the western sky after sunset. Observers in
northerly latitudes will see Venus set three hours after sunset but for those further south there is a shorter period of visibility.
The planet will be occulted by a two-day old waxing crescent Moon on the 16th
May and the two objects will form a classic pairing in the twilight sky as dusk falls.
On the 8th June 2004, Venus was at inferior conjunction
and transited the sun. Transits of Venus are rare, taking place at greater
than 100 year intervals and usually in pairs. The last two transits of Venus were in 1874 and 1882. June's transit
began at 7.20h and lasted 6 hours until 13.20h, the total event visible from Europe as a small black disc crossing
the lower part of the Sun from left to right. The next transit will be in late June 2012. After that, transits of Venus
won't occur again until 2117 and 2125.
Before and after inferior conjuction, when Venus is
the closest it comes to the Earth, are the times at which the planet is most brilliant and can be seen setting or rising
4 hours after or before the Sun. The dates of the next two inferior conjunctions are October 28th 2010 and October 26th 2018.
Mars continues to be visible in the evening sky, against the background of
. During May it decreases in brightness from +0.7 to +1.0 magnitude.
At opposition on the 28th August 2003, Mars was only 56 million kilometres from the Earth. It showed a
disc of 25.1 seconds of arc across which is almost as large as it can ever appear. Mars started 2003 at 310 million kilometres from
the earth at 4.5 seconds of arc and 1.6 magnitude. By opposition it brightened 50 times to reach -2.9 magnitude but faded to 0
magnitude by December. Even to the naked eye Mars was a striking object in the summer and autumn sky, easily identifiable by its
reddish hue in an area of sky poor in bright stars. Mars will not be as close again until 2018.
These favourable oppositions occur every 15 or 17 years but other oppositions occur at average intervals of 2 years 2 months during
which time the planet makes a complete circle of the Earth. In general Mars is observable every other year, being too close to the sun for favourable conditions
during other times. Brightness at opposition varies from -1.0 to -2.9 magnitude, and when furthest from the earth it fades to 1.7 magnitude. The planet can be
identified by its orange-red colour.
As in 2003, Mars comes nearest to the Earth at oppositions at the end of August. At these times it can be brighter than Jupiter,
although low in the sky in Aquarius for northern observors. In the northern hemisphere, the planet may be better seen at oppostions during autumn and winter months
when it is higher in the sky.
At magnitude -2.2, Jupiter is now visible low in the south-eastern sky before dawn. For
observors in equatorial and southern latitudes, the planet rises several hours before the Sun and dominates the eastern sky in the early morning hours. During
May Jupiter moves from Aquarius into Pisces.
Varying from 603 (at its closest) to 770 million kilometres from the sun, the difference in brightness between opposition and conjunction varies less than
with Mars, from about -2.9 to -1.8 magnitude. Always a bright planet, Jupiter comes to opposition a month later each year, moving approximately from one zodiacal
constellation to the next.
The 4 largest moons of Jupiter are easily visible through a small telescope, ranging from 4.6 to 5.6 in magnitude. The innermost, Io, takes 1.8 days
to orbit the planet making its motion easily detectable within a few minutes.
Saturn is an evening object in Virgo
throughout May, setting in the early morning hours. Saturn´s brightness decreases from +0.8 to +1.0 during the month as the ring angle decreases to 1.7º.
The planet reaches its second stationary point on May 31st, after which it resumes direct
Saturn moves more slowly than Jupiter and can remain in the same constellation for several years. The brightness of the planet depends on the
aspect of its rings, as well as its distance from Earth and the Sun.
The planet crossed the equator into the northern hemisphere in 1996 where it will remain until 2010 with the southern side of the ring system
facing the earth. Because of its distance, its brightness varies little between opposition and conjunction but is affected by the huge ring system. Seen edge on the
rings contribute little or no light.
Every 15 years the plane of Saturn's rings passes through the sun, illuminating first the north and then the south side. For a few days the
rings are edge on to the sun. About the same time the Earth passes through the ring plane and, depending on the Earth's position, this may happen just once or 3 times.
During 1995/96 there was a triple crossing and the next will be 2038/39. The next single crossings will be in 2009 and 2025.
Saturn's largest moon, Titan, is visible in small telescopes orbiting outside of the ring system.
Brightness varies slightly, reaching a maximum of +5.6 magnitude at opposition. This is bright
enough to see with the naked eye but identifying it against the stars is difficult. At closest approach, Uranus is 2,856 million kilometres (1,775 million miles)
Neptune has an average magnitude of 7.9 which varies little with changing distance. At its closest,
Neptune is 4,341 million kilometres (2,697 million miles) from Earth.
No longer an offical planet and never brighter than +13 magnitude, Pluto is only visible through powerful telescopes.
Last quarter: 6th
New moon: 14th
First quarter: 20th
Full moon: 27th